The invention relates to crankcase assemblies for reciprocating machines, and in particular to crankcases having at least one cylinder with a wet cylinder liner arrangement. The invention is suitable for stationary or mobile use, including commercial vehicle reciprocating compressors having a wet cylinder liner. Such liners are used in particular in die casted crankcases, for example pressure die casted aluminum crankcases.
In such a crankcase assembly a cylinder head for charging and discharging pressurized gas is mounted on the crankcase. A cylinder head gasket for preventing leakage of pressurized gas out of the cylinder is arranged at the cylinder head, circumferentially spaced from the inner wall of the cylinder liner. A circumferential coolant channel is formed between an inner crankcase wall and an outer wall of the cylinder liner. A lower sealing arrangement is provided between the inner crankcase wall and the cylinder liner on the crankshaft side of the coolant channel to inhibit leakage of coolant. A first upper sealing arrangement is provided between the inner crankcase wall and the cylinder liner on the cylinder head side of the coolant channel to inhibit leakage of coolant to the cylinder head side.
In one design of pressure die casted aluminum crankcases having wet cylinder liners, the liners are inserted into the crankcase cylinder only after the casting process, which allows for a less complex casting process. In such a design, the cylinder liners are usually inserted into the cylinders of the crankcase with an interference fit, with coolant channels surrounding the region of the cylinder running surface of the wet cylinder liner. The outer wall of the liner and the crankcase cylinder form a ring shaped room for the coolant fluid. The liner is in direct contact with the coolant fluid, hence called a wet liner.
For example in commercial vehicle compressor applications, the coolant fluid is supplied by the heavy duty engine to which the gear driven compressor is connected. A typical coolant pressure delivered by such engines is in the range of up to 3.5 bar (50.8 psi) relative. Some newer engines are designed for coolant pressures up to 6.5 bar (94.3 psi). Further, depending on the number and type of further auxiliary equipment to be cooled, coolant pressures temporarily may even go further up. Additionally, the oscillating pressure of the gas pressurized within the cylinder acts on the sealing means which is arranged between the inner crankcase wall and the cylinder liner on the cylinder head side. These higher pressures increase the potential for leakage of prior sealing designs, for example as a result of worn sealing means at the cylinder head side permitting leakage of pressurized gas into the coolant channel. Further, these higher pressures may overload lower sealing means between the inner crankcase wall and the cylinder liner on the crankshaft side of the coolant channel, potentially resulting in coolant leakage into the reciprocating machine oil circuit.
Known reciprocating machines often provide cast in liners to minimize the potential for leakage. This solution is not applicable for pressure die casting crankcases, as a core for the water channel cannot be removed after casting. It is also known to use steel beaded cylinder head gaskets for sealing the oscillating gas pressure within the cylinder; however, if the sealing means of the cylinder head gasket is arranged close to the inner diameter of the liner while the cylinder head bolts are at a radial distance to the gasket sealing means, moment loads can cause an umbrella-like deformation of the cylinder head (more precisely, of the valve plate arranged at the cylinder head gasket). This creates a risk for loosened bolts during use. A further risk is that the cylinder liner deforms in a way that oil can pass the piston rings and be carried by the gas compressed by the compressor into the brake system.
Therefore, it is an object of the present invention to overcome the disadvantages of the known designs and to provide an enhanced crankcase assembly for a reciprocating machine.
The present invention provides a crankcase assembly for a reciprocating machine, with a crankcase having at least one cylinder having a wet cylinder liner arranged therein. A cylinder head for charging and discharging pressurized gas is mounted on the crankcase and a cylinder head gasket for preventing leakage of pressurized gas out of the cylinder is arranged between the crankcase and the cylinder head. The cylinder head gasket is circumferentially spaced from the inner wall of the cylinder liner.
A circumferential coolant channel is formed between the inner crankcase wall and an outer wall of the cylinder liner, wherein a lower sealing arrangement is provided between the inner crankcase wall and the cylinder liner on the crankshaft side of the coolant channel to prevent coolant leakage from the coolant channel into the crankcase (and the oil therein). A first upper sealing arrangement is provided between the inner crankcase wall and the cylinder liner on the cylinder head side of the coolant channel to prevent coolant leakage to the cylinder head side. Separate from the first upper sealing arrangement, a second upper sealing arrangement is provided to prevent pressurized gas affecting the first upper sealing arrangement.
As indicated above, a crankcase assembly for a reciprocating machine, with at least one cylinder comprising a wet cylinder liner arranged therein is provided. Such a cylinder liner is known as “wet” cylinder liner as coolant flows along its outer wall for cooling the running surface of the piston within the cylinder. In the following, for simplification, the wet cylinder liner is also referred to as a “cylinder liner” or a “liner.”
The crankcase assembly includes a cylinder head mounted on the crankcase for charging unpressurized gas into the cylinder and for discharging pressurized gas out of the cylinder. The cylinder head usually includes a valve plate having valves provided on top of the cylinder space for the control of the charging and discharging of gas. In the description of the present invention no distinction will be made among the valve plate and the cylinder head, as the valve plate is considered to be an element of the cylinder head.
Between the cylinder head and the crankcase, a cylinder head gasket is arranged which provides sealing to prevent leakage of pressurized gas out of the cylinder. In one example, the cylinder head sealing arrangement is a bead is circumferentially spaced from the inner wall of the cylinder liner, thereby establishing a seal between the top surface of the crankcase and/or the top surface of the cylinder liner and the surface of the cylinder head facing the top surface of the crankcase and/or the top surface of the cylinder liner. With the sealing arrangement of the cylinder head gasket also running spaced from the outer wall of the cylinder liner, the pressurized gas acts on the contact area between the crankcase wall and the cylinder liner.
A circumferential coolant channel is formed between the inner crankcase wall and an outer wall of the cylinder liner. A coolant fluid under high pressure is guided through the coolant channel for cooling the running surface of the cylinder adjacent to the compressor piston reciprocating within the cylinder liner. Depending on the embodiment, the coolant channel may be ring-shaped and extend axially over a portion of the axial length of the cylinder liner sufficient to provide a desired cooling capacity. A lower sealing arrangement is provided between the inner crankcase wall and the cylinder liner to prevent coolant leakage to the crankshaft side of the crankcase. The lower sealing arrangement may be formed by a sealing ring such as an O-ring or the like, and may be provided in a circumferential groove in the cylinder liner wall or in the inner wall of the crankcase. Likewise, the lower sealing arrangement may be formed by an adhesive or another suitable sealing substance which is applied on the mating surfaces of the cylinder liner and the crankcase cylinder. Also, the lower sealing arrangement may be provided by the interference fit between the cylinder liner wall and the inner wall of the crankcase, for example, by including circumferential spring-back grooves on the cylinder liner wall or the inner wall of the crankcase, into which material of the opposite mating surface penetrates to form a seal. The lower sealing arrangement also may be formed by any other appropriate configuration of materials and/or contours between the inner crankcase wall and the cylinder liner inserted therein that prevents coolant leakage into the crankshaft side of the crankcase.
A first upper sealing arrangement is provided between the inner crankcase wall and the cylinder liner on the cylinder head side of the coolant channel to prevent coolant leakage to the cylinder head side. The first upper sealing arrangement may be formed by a sealing ring such as an O-ring or the like provided in a circumferential groove in the inner crankcase wall or in the cylinder liner wall, for example, by including surfaces of a circumferential shoulder of the cylinder liner adjacent to the wall of the crankcase cylinder. The first upper sealing arrangement also may be formed by a sealing substance applied between the inner crankcase wall and the cylinder liner on the cylinder head side of the coolant channel, or by any other suitable configuration of materials and/or contours between the inner crankcase wall and the cylinder liner inserted therein that prevents coolant leakage on the cylinder head side of the coolant channel.
The first upper sealing arrangement is present to prevent coolant leakage to the cylinder head side, and is therefore exposed to the pressure of the coolant fluid. From the cylinder head side, the oscillating pressure of the gas pressurized within the cylinder acts on the contact area between the inner crankcase wall and the outer wall of the cylinder liner. In order to prevent the oscillating gas pressure acting on the first upper sealing arrangement, a second upper sealing arrangement is provided separate from the first upper sealing arrangement. The second upper sealing arrangement is provided separate to the first upper sealing arrangement to prevent interaction of the coolant pressure and the oscillating pressure of the gas affecting the first upper sealing arrangement. Specifically, the second upper sealing arrangement is arranged to prevent the pressurized gas from penetrating the contact area between the inner crankcase wall and the outer wall of the cylinder liner up to the position of the first upper sealing arrangement.
In one embodiment of the crankcase assembly, the second upper sealing arrangement is provided between the inner crankcase wall and the cylinder liner. The second upper sealing arrangement may be formed by a sealing ring such as an O-ring or the like provided in a circumferential groove in the inner crankcase wall or in the cylinder liner wall, for example, by including the surfaces of a circumferential shoulder of the cylinder liner adjacent to the wall of the crankcase cylinder. The second upper sealing arrangement also may be formed by a sealing substance applied between the inner crankcase wall and the cylinder liner on the cylinder head side of the first upper sealing arrangement, or by any other suitable sealing arrangement between the inner crankcase wall and the cylinder liner on the cylinder head side of the first upper sealing arrangement that prevents pressurized gas from acting on the first upper sealing arrangement.
In one embodiment of the crankcase assembly, the cylinder liner includes a radially protruding circumferential shoulder, in particular on the cylinder head side of the coolant channel. When mounted to the crankcase, the shoulder is arranged in a corresponding recess of the inner crankcase wall. Thus, the shoulder enhances the assembly of the cylinder liner within the crankcase by assisting in defining the axial position of the liner within the crankcase cylinder. In crankcase assemblies of the present type, the cylinder liner is inserted only after casting. In many applications the crankcase cylinder-to-cylinder liner interface is an interference fit which is created via a shrinking process. Such an interference fit may be designed such that a sealing connection between the cylinder liner and the inner wall of the crankcase cylinder is established.
In one embodiment of the crankcase assembly, the first upper sealing arrangement and/or the second upper sealing arrangement is provided between the circumferential shoulder of the cylinder liner and the inner crankcase wall. In an embodiment with the circumferential shoulder arranged in a corresponding recess of a cylinder wall, the first upper sealing arrangement and/or the second upper sealing arrangement is arranged between the outer wall of the circumferential shoulder of the cylinder liner and the corresponding wall of the recess of the cylinder wall. In an embodiment with the radially protruding circumferential shoulder of the cylinder liner arranged at the top end of the cylinder liner, this design provides for a coolant channel that extends up to the circumferential shoulder. This enables cooling of the surface along which the piston moves up to the position of the circumferential shoulder. In a design with both the first and second upper sealing arrangements provided between the circumferential outer wall of the radially protruding circumferential shoulder of the cylinder liner and the corresponding recess of the inner crankcase wall (with the first upper sealing arrangement being separate from the second upper sealing arrangement), a cost-efficient parallel manufacture and assembly of both upper sealing arrangements is possible.
In a further embodiment of the crankcase assembly, the second upper sealing arrangement is provided on the cylinder head side of the cylinder liner, in particular on the axial end face of the cylinder liner. In such a design, the pressurized gas is prevented from acting on the contact area between the inner crankcase wall and the outer wall of the cylinder liner. In one optional design, the sealing arrangement is arranged in a circumferential step in the axial end face of the cylinder liner or in the axial end face of the crankcase surrounding the cylinder liner. This design enables the second upper sealing arrangement to be provided in such a way that it forms a seal between the axial end face of the cylinder liner and the cylinder head and at the same time it forms a seal between the radial surface of the cylinder liner and the outer wall of the recess in the inner crankcase wall.
In a further embodiment of the crankcase assembly, the second upper sealing arrangement is formed by the cylinder head gasket. In such a design, the cylinder liner includes at its cylinder head side a radially protruding circumferential shoulder having an enlarged diameter to enable the arrangement of the seal (e.g., a sealing bead) of the cylinder gasket both at a distance from the inner diameter of the cylinder liner and also close to the cylinder head bolts. This design provides reliable protection against leakage of pressurized gas which could affect the first upper sealing arrangement, without creating a risk for loosened bolts.
In a further embodiment of the crankcase assembly, the first upper sealing arrangement and/or the second upper sealing arrangement and/or the lower sealing arrangement is provided in a circumferential groove formed in the outer wall of the cylinder liner or in a circumferential groove formed in the inner crankcase wall. Depending on the type of the sealing and/or the available manufacturing processes, the provision of more circumferential grooves formed at the outer wall of the cylinder liner or in the inner crankcase wall may be possible. The provision of circumferential grooves for the sealing arrangement at the same wall (either at the outer wall of the cylinder liner or the inner crankcase wall) is advantageous in that there is no requirement to further machine the surface opposite to the respective groove for many types of seal arrangements.
In a further embodiment of the crankcase assembly, the first upper sealing arrangement is provided between a chamfer arranged at the crankshaft side of a radially protruding circumferential shoulder of the cylinder liner and a corresponding recess of the cylinder wall in which the circumferential shoulder of the cylinder liner is arranged. Such a design enables an easy manufacture of the chamfer as a groove for the sealing arrangement and a simplified mounting of the sealing arrangement, as the recess for receiving the circumferential shoulder formed in the inner crankcase wall is usually easy to access. As this design provides for two sealing surfaces (in particular axial and radial), the sealing effect of such a design is improved.
In a further embodiment of the crankcase assembly, the first upper sealing arrangement and/or the second upper sealing arrangement is an O-ring seal, a V-seal, X-seal, quad-ring-seal, and/or a ring-seal with any other suitable cross-section geometry. The first upper sealing arrangement and/or the second upper sealing arrangement may also include any other suitable type of sealing, for example, a sealing fluid, a viscous sealing material and/or a pasty sealing material. The use of O-rings in an upper sealing arrangement is for example a cost-efficient option for providing reliable sealing.
In a further embodiment of the crankcase assembly, at least one venting channel is arranged between the first and second upper sealing arrangements for venting any pressurized gas which seeps through the second upper sealing arrangement and for draining of coolant fluid which seeps through the first upper sealing arrangement. With the at least one venting channel, an interaction between the first and second upper sealing arrangements, in particular a negative effect of pressurized gas which overcomes the second upper sealing arrangement on the first upper sealing arrangement, is prevented. One embodiment of the at least one venting channel connects the area between the first and second upper sealing arrangements with the environment outside the crankcase. In one embodiment the at least one venting channel is connected to a detector which serves for an early detection of malfunction of one of the first and second upper sealing arrangements.
The invention further provides a reciprocating compressor having a crankcase assembly of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.